Metamict Radiation Damage in ^ Single Crystals Pranesh Sengupta (sengupta@barc.gov.in) BARC, Mumbai India
Why such study is required? • To document collective effects of different radiations ( α , β , γ ) on different matrices (silicate, aluminosilicate, phosphate) having relevance in waste immobilization over long time scale. • To understand and predict radiation effects on medium/short range ordering of vitreous wasteform and crystalline components of glass ceramics and ceramic wasteforms. • To document relative dominance of radiation damage and thermal annealing. • To establish radiation effects – matrix composition – matrix structure – properties correlations. • To build-up public confidence on vitrified nuclear waste matrices.
Atlas of METAMICT Natural Single Crystals Cordierite (Mg, Fe) 2 Al 3 (Si 5 AlO 18 ) Gadolinite ( Y 2 FeBe 2 Si 2 O 10 ) Zircon Halite Apatite (ZrSiO 4 ) (NaCl) (Ca 10 (PO 4)6 (OH,F,Cl) 2 , )
Metamictization is a natural process of CRYSTALLINE to AMORPHOUS phase transformation Outcome of two counteracting processes: radiation damage accumulation & thermal annealing . Some mineral species ( zircon, thorite, pyrochlore, fergusonite ) commonly become metamict . Others ( huttonite, monazite, uraninite, apatite ) are mostly observed in crystalline state , even though often being experienced similar radiation doses.
Johan Gadolin (5 June 1760 – 15 August 1852) was a Swedish later Finnish chemist, physicist and mineralogist. Gadolin discovered a "new earth" containing the first rare-earth compound yttrium, which was later determined to be a chemical element. He is also considered the founder of Finnish chemistry research. He extracted Y (1794) from a glass like natural material, which was later named as ‘ gadolinite ’ after him.
Jacob Berzelius (Swedish; 20 Aug 1779 – 7 Aug 1848), isolated several new elements including cerium and thorium. J Berzelius extensively studied natural minerals including gadolinite and reported about its ‘ pyrognomic behaviour ’, which upon heating exhibited sudden glowing followed by shattering into pieces . Waldemar Christofer Brøgger (10 Nov. 1851 – 17 Feb. 1940, Norway) first used the term ‘ metamikte ’, in the year 1893 , as a class of naturally occurring amorphous materials . Br φ gger speculated that metamictization was due to “ outside influences ” and that complicated structures might be more susceptible to this effect. Spencer (1904) considered hydration as a possible cause , as the molecular water content of these phases could be exceedingly high (10 – 15wt%).
Other workers during the second half of the 19 th century (~1860s) established that these phases were initially isotropic but become birefringent and increase in specific gravity on heating . As this work predated the discovery of radioactivity in 1896 by Becquerel, metamictization was not recognized as radiation induced transformation.
Tabulated the changes in properties (e.g. release of stored energy Adlof Pabst (1899-1990) and decreased resistance to leaching) which resulted from the Univ. of California, Berkeley radiation damage. Pabst specifically noted that some structures are ‘resistant’ to damage accumulation (e.g. Monoclinic ThSiO 4 ) while other polymorphs are often found in the metamict state (e.g. Tetragonal ThSiO 4 ). ThO 9 Coordination Polyhedra ThO 8 Coordination Polyhedra Monoclinic, P2 1 /n Tetragonal, I4 1 /amd Isostructural Monazite Isostructural Zircon NEVER Metamict Partially/completely Metamict a = ~6.784Å, b = ~6.974Å, c = ~6.500Å, β = 104.92 0 a = b = ~7.1328 Å, c = 6.3188Å , β = 104.92 0
Huttonite Monoclinic V: 30.4Å 3 SiO 4 ThO 9 T>1225 o C Thorite T<1225 o C Tetragonal Th site expansion Higher volume Lower symmetry V: 25.2Å 3 ThO 8 Both phases occur naturally, but show markedly different behavior toward metamictization
Thorite vs. Huttonite: ThSiO 4 Stability criteria based on radius ratio and charge balance are inconclusive; the Th/O radius ratio (0.76) suggests that the ninefold coordinated huttonite structure should be preferred, while a calculation of Pauling charge balance indicates that O(1) of huttonite is overbonded ( ζ = 2.5). All O atoms in thorite are exactly charge balanced ( ζ = 2.0). Irradiated powders of monoclinic huttonite and tetragonal thorite, with Ar + ions at 3 MeV to investigate structural controls on radiation damage. Using XRD analysis, it was demonstrated that both thorite and huttonite can become metamict (the damage cross-section for thorite is nearly twice that of huttonite); however, low temperature annealing studies showed that the huttonite recrystallized more easily than thorite. Under ambient conditions over geologic time, huttonite may recrystallize; therefore, huttonite is not found in the metamict state .
Various waste forms Crystalline ceramics Fe-Cr-Ni-Zr Alloy ThO 2 ZrO 2 Sphene glass ceramics Sodium barium borosilicate glass
Wasteform Selection Criteria Homogeneous Microstructure Solubility limit, waste loading, uncontrolled crystallization Chemical durability Leaching Available Technology Processing temperature
Waste glass system: Sodium borosilicate glass Na 2 O Unfused mass X 900 2Na 2 O. SiO 2 800 700 2Na 2 O. B 2 O 3 Na 2 O. SiO 2 No glass forming zone m 3 Homogeneous glass Na 2 O. B 2 O 3 900 800 √ Na 2 O. 2B 2 O 3 Glass forming zone Na 2 O. 3B 2 O 3 m 2 Na 2 O. 4B 2 O 3 700 800 700 m 1 Immiscibility zone 1300 1000 800 900 Liq.-liq. immiscibility 50 100 SiO 2 B 2 O 3 10 20 30 40 60 70 80 90 X Sodium Borosilicate glass
Chemical durability assessments: P - T dependence 90 ° C, 1 atm, 710 days 400 ° C, 2 Kb, 2 hour
After 2 years leaching Si K α 8000 Altered layer Pristine Smectite Intensity (cps) Leachant Surface layer Saponite glass Pristine glass Natrolite Leached matrix 0 0 200 Distance (µm)
Indigenous development of vitrification technology Metallic melter pot Ceramic melter pot Cold crucible Proven technology Proven technology Demonstration stage Induction heating Induction heating Joule heating ~1000 o C ~1150 o C ~1500 o C Borosilicate glass Borosilicate glass Aluminosilicate glass
Pre-mature degradation of furnace may also influence matrix selection! Alloy 690 Glass NiCrO 4 Clean freeze valve Process pot √ Crack Vapor Cr 23 C 6 Cr 2 O 3 (Fe,Ni)Cr 2 O 4 Reaction zone (192 hrs) Melt X Glass 3.0 Glassy layer 2.8 x = kt 1/1.28 2.6 Enrichment 2.4 Clogged f.v. 2.2 ln x ln x Depletion 2.0 1.8 1.6 1.4 Cr depleted zone 1.2 7 8 9 10 11 12 13 x = 10.9 x 10 -6 + 1 x 10 -8 t 1/2 m ln t ln t
The Problem: Structural analysis by 29 Si & 11 B NMR Borosilicate glass Borosilicate glass + 14 mol% NaF (Q 3 : 78%, Q 2 : 22%; BO 4 : 48%, BO 3 : 52%) - U & Al polymerizes the network further, - PGE and TiO 2 promotes crystallization. The feasible solution: Glass Ceramics
Radiation damage in Single Natural Crystals Gadolinite ( Y 2 FeBe 2 Si 2 O 10 )
Natural amorphous material -conchoidal fracture, -Isotropic optical properties,
However this methodology dose not work for partially metamict minerals!!! Metamictized domain Zircon (ZrSiO 4 ) Holland and Gottfried (1955) reported that intermediate zircons having densities between about 4.6 and 4.1 gm. cm -3 ( ~4.7 gm cm -3 for non-metamict zircon).
Cordierite (Mg, Fe) 2 Al 3 (Si 5 AlO 18 ) α damage Source of α nuclide In 1914, A. Hamberg, based on the observation of pleochroic haloes, first suggested that metamictization is a radiation- induced, periodic-to-aperiodic transition caused by α - particles which originate from decay of constituent U and Th.
Halite in nature
Dose coloration always imply RADIATION effects? Milky Fluid Blue white inclusions Pink / hematite Violet Cl - removal Red needles Radioactive Non- by ionization Orange Sylvite (KCl) Purple Origin Radioactive radiation paticles150- 180 nm Origin Yellow Sulphur Dark particles 130- blue 150 nm Green Chloritic clay Brownish Organic particles 110- black matter 120 nm
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